Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $64.77   13.683%   $73.6325   $73.63   $73.65   $73.60  
  Purchase #2 $94.65   11.454%   $105.4912   $105.49   $105.50   $105.50  
  Purchase #3 $61.93   13.202%   $70.106   $70.11   $70.10   $70.10  
  Purchase #4 $27.81   13.864%   $31.6656   $31.67   $31.65   $31.70  
  Purchase #5 $177.51   8.672%   $192.9037   $192.90   $192.90   $192.90  
  Purchase #6 $204.89   13.552%   $232.6567   $232.66   $232.65   $232.70  
  Purchase #7 $129.35   8.437%   $140.2633   $140.26   $140.25   $140.30  
  7 purchase totals = $760.91       $846.7190   $846.72   $846.70   $846.80